Electrolytic deposition

ABSTRACT

An electrolytic deposition process suitable for use where high deposition rates are required. A metallic powder which reacts with discharged anions is dispersed in the electrolyte adjacent the anode but is prevented from occurring in appreciable concentration in the electrolyte adjacent the cathode. The electrolyte may be arranged to flow continuously over the cathode surface. Specific conditions are disclosed for carrying out the process when depositing nickel, and an apparatus is described for utilizing the process in the electroforming of metallic articles.

O United States Patent 1111 3,617,449

[72] Inventors Maurice Eric Giles 3,251,764 5/1966 Miller etal. 204/252 X Cottenharn; 82,877 10/1868 Remington 204/285 X John George Waller, Sutton, both of 868,769 10/1907 Ehrenfeld et al. 204/252 X England 1,395,827 11/1921 Hybinette 204/264 X {21] Appl. No. 729,173 2,104,812 l/l938 Phillips 204/285 X [22] Filed May 15,1968 3,223,611 12/1965 Wells et a1. 204/49 X [45] Patented Nov. 2,1971 3,300,396 l/1967 Walker 204/49 [73] Assignee National Research Development FOREIGN PATENTS 763,941 7/1967 Canada 204/282 England 765,384 8/1967 Canada 204/49 [32] Priority May 19, 1967 [33] Great Britain OTHER REFERENCES [31] 23,476/67 W. A. Wesley et al., 36th Annual Proceedings of the American Electroplaters' Society, p. 91, 1949).

El. Roehl et al., Plating, pp. 142 14684 171, Feb. 1950. [54] ELECTROLYTIC DEPOSITION 3 Claims, 1 Drawing g Primary Examiner-G. L. Kaplan Attorney-Cushman, Darby & Cushman [52] US. Cl 204/3, 204/14 R, 204/49, 204/45 R, 204/252, 204/260, 204/263 [51] IIILCI C2311 7/00, ABSTRACT: An electrolytic deposition process i bk f C23) 5/02 C23) 5/68 use where high deposition rates are required. A metallic [50] Field of Search 204/252, powder which reacts with discharged anions is dispersed in [he 26L 262126312641 28418212851 electrolyte adjacent the anode but is prevented from occur- 14145 ring in appreciable concentration in the electrolyte adjacent the cathode. The electrol te ma be arran ed to flow continu- [56] Reerences Cited ously over the cathode s urface Specific conditions are dis- UNITED STATES PATENTS closed for carrying out the process when depositing nickel, 2,872,406 2/1959 Buchanan 204/282 x and an apparatus is described for utilizing the process in the 3,135,674 6/1964 Ruetschi 204/252 X electroforming of metallic articles.

ELECTROLYTIC DEPOSITION This invention relates to electrolytic deposition, and has as one object the provision of a process which is suitable for use where high deposition rates are required, for example in the electroforming of articles.

According to the invention, in an electrolytic deposition process that part of the electrolyte in the immediate vicinity of the anode has dispersed in it a substantial concentration of a powder of metallic material which will react with discharged anions of the electrolyte, the concentration of said powder in that part of the electrolyte in the immediate vicinity of the cathode being much smaller.

In such a process the provision of the powder results in an increase of the effective anode surface area above that of the anode proper, thereby reducing the anode-cathode voltage for a given cathode current density and making it possible to use relatively high values of cathode current density without incurring too rapid a rate of depletion of the electrolyte. The invention is particularly useful in connection with processes of the kind in which a high deposition rate is achieved by causing the electrolyte to flow continuously over the cathode surface at a relatively high velocity.

The required concentration gradient for the powder may be achieved by interposing between the anode and cathode a barrier which is permeable to the electrolyte but is substantially impervious to the powder; if desired the barrier may be given an appropriate geometrical form so as to influence the distribution of the deposited material on the cathode surface, in a manner similar to that which may be achieved by shaping of the anode in a conventional electrolytic deposition process. Alternatively, it is contemplated that the required concentration gradient may be achieved by techniques similar to those used in connection with fluidized beds.

ln some cases a small concentration of the powder may be deliberately incorporated in that part of the electrolyte in the immediate vicinity of the cathode, so that the deposit on the cathode is formed by a combination of electrolytic and cataphoretic action; it may in such cases be desirable for the deposit to be subsequently compacted by a suitable mechanical process such as rolling. Even where no powder is initially incorporated in the pan of the electrolyte in the immediate vicinity of the cathode, in practice some fine particles of the powder may reach this part of the electrolyte, since however coarse are the original particles of the powder dispersed in the part of the electrolyte in the immediate vicinity of the anode they will gradually be reduced in size as the process proceeds. This will not normally give rise to any deleterious effects; in fact the presence of fine particles of the powder in the immediate vicinity of the cathode may improve the quality of the deposit particularly in cases where a relatively high deposition rate is used.

If necessary, however, it should be possible to arrange for a flow of the electrolyte to occur in the anode region in such a manner that fine particles are removed from the system before they can reach the part of the electrolyte in the immediate vicinity of the cathode.

Where a deposit of uniform composition is required the material of the powder will of course have the same composition as that which would be deposited from the electrolyte in the absence of the powder. If desired, however, the composition of the powder may be made different from that of the material initially deposited from the electrolyte, so that as the powder is dissolved into the electrolyte in the course of the process a deposit will be obtained whose composition varies through its thickness.

As an example of the results which may be achieved by use of the invention, a description will now be given of experiments carried out on the deposition of nickel on copper from an electrolyte consisting of nickel fluoroborate solution of pH3 and specific gravity 38 Twaddell, maintained at a temperature of 60 C.

The experiments were carried out using a cell divided into two compartments by a planar membrane of porous polyvinyl chloride 0.75 millimeter thick and having a pore size of l2 microns. Respectively disposed in the two compartments were an anode in the form of a platinum wire, and a cathode in the form of a copper plate disposed parallel to and spaced 1.25 centimeter from the membrane. Both compartments were provided with inlet and outlet tubes, the solution being pumped through the tubes for the cathode compartment so that it flowed over the cathode surface at a velocity of about 6 meters per minute. Powdered nickel, having a particle size not greater than 50 microns and which had been elutriated to remove very fine material, was added to the solution in the anode compartment in concentrations of up to 1 gram of powder to l milliliter of solution, the resultant slurry being agitated by bubbling air through it and the inlet and outlet tubes of the anode compartment being provided with filters similar to the membrane to prevent any substantial escape of the powder.

Satisfactory deposits were obtained using various cathode current densities in the range 90-360 amperes per square meter. For any given value of cathode current density, it was found that the anode-cathode voltage decreased with increasing powder concentration over the range of concentrations used, the variation being approximately in accordance with an inverse exponential function. For example, for a cathode current density of I amperes per square meter, the anodecathode voltage decreased from about 36 volts in the case where no powder was added to about 7 volts in the case of a powder concentration of 1 gram per milliliter of solution.

An apparatus suitable for use in electroforming articles when using a method according to the invention will now be described with reference to the accompanying drawing, which is a sectional view of the apparatus in use.

The apparatus comprises a cell 1 of insulating material having an inlet 2 and an outlet 3, and provided with a removable cover comprising an annular part 4 and a separate plate 5 which fits over the aperture in the part 4. Within the cell 1 is fitted a tubular member 6 of insulating material which rests on a shoulder 7 formed in the cell 1. In use there is disposed centrally within the bore of the member 6 a former 8 on which metal is electrolytically deposited to form an article the deposit being subsequently separated from the former 8 in conventional manner. The former 8, whose surface conforms in shape to the article to be electroformed, is supported between an upper insulating member 9 having a flange which rests on the top of the member 6 and an insulating rod 10 which extends below the former 8 and whose lower end is located in a cavity formed in a block 11 secured to the base of the cell 1. The former 8 is provided with an insulated lead 12 which extends through the member 9 and passes out of the cell 1 through the plate 5.

Within the member 6 is formed an annular. recess 13 disposed vertically in register with the former 8, the space within the recess 13 being separated from the space surrounding the former 8 by a thin tubular membrane 14 of porous polyvinyl chloride, which is shaped to conform substantially with the surface of the former 8. Within the recess 13 is disposed a tubular electrode 15 formed of platinum wire mesh, the electrode 15 is conforming in shape with and being disposed close to the membrane 14. The electrode 15, which serves as an anode in the deposition process, is provided with an insulated lead 16 which extends through the member 6 and passes out of the cell 1 through the member 4,

ln operation, a suitable electrolyte 17 for deposition of the required metal is caused to flow continuously through the cell 1 from the inlet 2 to the outlet 3, the flow passing through the space between the former 8 and the membrane 14, at an appropriate velocity to enable satisfactory deposition to occur at a relatively high rate, and then through channels 18 provided in the member 9. A separate flow of the same electrolyte is passed through the recess 13 via ducts l9 and 20, formed in the member 6, which respectively communicate with inlet and outlet tubes 21 and 22 passing through the member 4. The electrolyte in the recess 13 has dispersed in it a powder of the metal to be deposited, the particle size being such that the powder cannot pass through the membrane 14; the dispersion is maintained in a state of agitation by the flow of the electrolyte through the recess 13. a filter 23 (which may be of the same material as the membrane 14) being provided at the entrance to the duct 20 to prevent the powder from being carried out of the recess 13. Deposition is effected by connecting a suitable power supply (not shown) between the leads l2 and 16 with polarity such as to maintain the electrode positive with respect to the former 8. It will be appreciated that the construction of the apparatus is such that the assemblies respectively incorporating the former 8 and the tubular member 6 can readily be inserted into and withdrawn from the cell 1.

We claim:

1. In an electrolytic process utilizing a cell containing an anode and cathode disposed in a metal-ion containing electrolyte wherein a current of electricity flows through the metal-ion containing electrolyte from the anode to the cathode and said metal is deposited on the cathode the improvement which comprises the steps of:

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a. dispersing particles of the metal in that part of the electrolyte which is in the immediate vicinity of the anode;

b. maintaining that part of the electrolyte in the immediate vicinity of the cathode relatively free of said metal particles by separating the cell into two compartments by means of a diaphragm with the anode being situated in the first compartment and the cathode in the second compartment, said diaphragm being impervious to said-metal particles and permeable to the electrolyte; and

c. maintaining a separate flow of electrolyte into and out of each compartment so that electrolyte flows over substantially the entire cathode and anode.

2. A process according to claim 1 in which the particles are of nickel and the electrolyte is a nickel fluoroborate solution.

3. A method of manufacturing a metallic article, comprising forming a metallic deposit on a former by a process according to claim 1, and then separating the deposit from the former in a coherent town to constitute the article.

t t i t i 

2. A process according to claim 1 in which the particles are of nickel and the electrolyte is a nickel fluoroborate solution.
 3. A method of manufacturing a metallic article, comprising forming a metallic deposit on a former by a process according to claim 1, and then separating the deposit from the former in a coherent form to constitute the article. 